I was in a meeting today, and the subject of weight loss came up. As some of you may know, I have previously written about how exercise tends not to be particularly effective for those wishing to shed pounds.
I made the point that those wanting to lose weight would do better to, among other things, eat a diet that is rich in foods that tend to sate the appetite quite effectively. There is some evidence that in this respect, protein is king.
One of the other usual keys to successful weight loss is to concentrate on eating a diet based on foods that tend not be stored as fat (avoiding the over-consumption of many carbs including bread, potatoes, rice, pasta and breakfast cereals is key here). What this amounts too, in effect, is a diet that is rich in protein and low in carb.
Such a diet is not for everyone, but I have to say over the years I’ve found it one of the most effective strategies for individuals wanting to improve their health, weight or wellbeing. I don’t know how many people I’ve had personal dealings with who say they have been freed from a life of yo-yo dieting and semi-starvation simply by eating a relatively protein-rich (and lower carb) diet.
There’s a growing number of studies that support this way of eating for successful weight control, and one example is a study published in January in the American Journal of Clinical Nutrition [1]. This study took a group of obese women (average age 49) and assigned them to one of two diets: high protein or high carbohydrate, for a period of 64 weeks (12 weeks of supposedly quite strict dieting followed by a year of less severe restriction). Both groups lost weight, but there was no significant difference between the two groups.
There’s one thing to instruct people what to eat, whether they do it or not is another matter. So, the researchers involved in this study attempted to check ‘compliance’ using a urinary test which gives an indication of the amount of protein the women ate. Because there was no significant difference in this measurement between the groups, the researchers concluded that compliance was likely to have been ‘poor’.
So, what the researchers did next was to get the dietary records of the women and calculate from them what they actually ate, including their protein intake. And that’s when things got more interesting. What they found was this:
The more protein the women ate, the more weight they lost.
The average weight loss for women who reported eating a high protein diet was 6.5 kg. In comparison, those eating a lower protein diet lost an average of 3.4 kg. Despite the fact that the protein-rich diet eaters lost almost twice as much weight as their lower-protein eating counterparts, this difference was not found to be ‘statistically significant’. This might have had something to do with the fact that the numbers of women who had their diets analysed was small (a total of 52). Despite this, the group eating a protein-rich diet were found to lose significantly more ‘peripheral’ fat (2.4 kg on average compared with 0.9 kg).
One reason for these generally improved outcomes from eating a protein-rich diet might be related to protein’s appetite-sating ability. However, when I checked the calorie intakes, I was surprised to find that the higher protein group ate significantly more calories (an average of about 170 calories more a day).
This finding first of all flies in the face of the idea that people eating a protein rich diet tend to eat less. And I have no explanation for it. Perhaps it had something to do with the fact the gathering data on what people eat is fraught with difficulty. However, what about if we take these results at face value? Let’s assume, for a moment, that the high-protein group ate more but lost more weight.
One explanation here is that the high-protein eaters were more active. Unfortunately, the study provides no data on activity levels. In view of the fact we have no evidence to the contrary, I’m tempted to assume that activity levels were the same.
Some would say this can’t be so, because it contravenes what is known as the ‘1st law of thermodynamics’ (which basically states that energy can’t be created or destroyed – only its form can be changed).
However, remember that one way to lose weight is to eat a diet that tends not to get stored as fat. The fat storage hormone in the body is insulin, which is secreted primarily in response to carbohydrate consumption. As expected, the protein-rich dieters actually ate generally less carbohydrate (and more fat, by the way) than their lower-protein eating counterparts.
So, it might have been that the higher protein, lower carb diet resulted in less fat deposition in the body. But if that’s the case, where might the energy that didn’t get stored as fat go?
Well, one thing we know is that when people eat more protein it increases what is known as ‘protein turnover’ in the body [2]. And there’s also evidence that when protein turnover increases, so does the body’s metabolic rate [3].
In short, there is at least some evidence suggests that when people eat more protein and less carb, less of what they eat is stored as fat, and the energy that appears to go ‘missing’ is simply burned by a more ‘efficient’ metabolism. When it comes to weight control, it might be that it’s more than just calories that count.
References:
1. Clifton PM, et al. Long-term effects of a high-protein weight-loss diet. American Journal of Clinical Nutrition 2008;87(1):23-29
2. PJ Garlick, et al. Influence of dietary protein intake on whole-body protein turnover in humans. Diabetes Care 1991;14(12):1189-1198
3. Welle S, et al. Relationship of resting metabolic rate to body composition and protein turnover. Am J Physiol 1990;258(6 Pt 1):E990-8
